Set of humeral components for total shoulder prosthesis

ABSTRACT

In this set of humeral components for a total shoulder prosthesis, each component is formed by an anchoring stem and a metaphyseal part which defines a concave surface of articulation globally in the form of a portion of sphere. The offset between the axis of symmetry of this surface and the central axis of the metaphyseal part of the different components is variable. This makes it possible to limit or to avoid, by a reasoned choice of the humeral component used, an interference with the pillar of the scapula during the movement of adduction.

FIELD OF THE INVENTION

The present invention relates to a set of humeral components for a total shoulder prosthesis, as well as to a prosthesis and to a method for installing such a prosthesis.

BACKGROUND OF THE INVENTION

In the domain of total shoulder prostheses, it is known, for example from U.S. Pat. No. 3,978,528, from EP-A-0 299 899 or from FR-A-2 836 039, to constitute a prosthesis in which a convex articular surface is fast with the glenoid cavity, while a concave articular surface is fast with the humerus, the cooperation of these surfaces making it possible to recreate a joint at the level of the shoulder. With these known prostheses, it may happen, during the movement of adduction, that a portion of the metaphyseal part of the humeral component hits the pillar of the scapula, which limits this movement and may prove painful, and even cause unsealing of the prosthesis.

It is a more particular object of the present invention to overcome these drawbacks by proposing a set of humeral components which allows the surgeon to optimize the relative positioning of the prosthetic components, as a function of the patient's anatomy.

SUMMARY OF THE INVENTION

In that spirit, the invention relates to a set of humeral components for a total shoulder prosthesis, in which each component is formed by an anchoring stem and a metaphyseal part which defines a concave surface of articulation globally in the form of a portion of sphere. This set of components is characterized in that the offset between the central axis of the metaphyseal part and the axis of symmetry of the concave surface of articulation of the different components is variable.

Thanks to the invention, the concave articular surface of the different humeral components may be so positioned, with respect to the outer surface of the metaphyseal part, that the interferences of the metaphyseal part with the pillar of the scapula are minimized, and even eliminated.

According to advantageous but non-obligatory aspects, a set of humeral components may incorporate one or more of the following characteristics, taken in any technically admissible combinations:

For each component, the axis of symmetry of the articular surface and the central axis of the metaphyseal part are substantially parallel.

For at least one of these components, the axis of symmetry of the articular surface is disposed, with respect to the central axis of the metaphyseal part, opposite a median axis of the anchoring stem. In that case, the surface of articulation of at least one of these components advantageously extends up to the immediate vicinity of the edge of the metaphyseal part, and is even intersected by this edge, opposite that part of the edge located globally in line with the anchoring stem.

The different components have substantially the same shape, except for the position of the articular surface in the metaphyseal part.

The angle of inclination of the axis of symmetry of the articular surface with respect to the median axis of the stem has substantially the same value for all the components.

The afore-mentioned offset may be zero for one of the humeral components, the axes in that case being merged.

The invention also relates to a total shoulder prosthesis which comprises a humeral component selected from a set of components as described hereinabove. Such a prosthesis is more easily adaptable to the patient's morphology.

According to an advantageous aspect of the invention, such a prosthesis comprises, in addition, a glenoidal component which forms a convex surface of articulation centred on an axis of symmetry which is not perpendicular to a rear face of this component intended to come into abutment against the glenoid cavity. This aspect of the invention makes it possible to “compensate” a defect in parallelism between the resectioned surface of the glenoid cavity against which the glenoidal component abuts and the axis of the patient's spinal column.

Finally, the invention relates to a method for installing a total shoulder prosthesis which comprises steps consisting in:

preparing the bones with a view to positioning a glenoidal component and a humeral component;

installing on the glenoid cavity a glenoidal component defining a convex articular surface;

selecting, from a set of humeral components, a humeral component provided with a concave articular surface adapted to cooperate with a convex articular surface of the glenoidal component, this component substantially not interfering or interfering only little with the pillar of the scapula during a movement of adduction, and

installing the humeral component on the humerus.

The method of the invention may be carried out by a surgeon installing a total shoulder prosthesis, the selection of the most adapted humeral component being able to be effected during the surgical operation, or in advance during the pre-op check-up.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more readily understood and other advantages thereof will appear more clearly in the light of the following description of a set of humeral components in accordance with its principle and of the installation of a total shoulder prosthesis by means of this set of components, given solely by way of example and made with reference to the accompanying drawings, in which:

FIG. 1 schematically shows a total shoulder prosthesis installed on a patient and comprising a humeral component shown in section, issuing from a set of components according to the invention.

FIG. 1A is a view of detail A in FIG. 1 in configuration of interference between the humeral component and the pillar of the scapula.

FIG. 2 is a view similar to FIG. 1, whereas the humeral component is different from the one used in the prosthesis of FIG. 1.

FIG. 3 schematically shows a set of humeral components according to the invention, shown in section, and

FIG. 4 is a view similar to FIG. 1A for a prosthesis of which the humeral component is identical to that of FIG. 2, the glenoidal component being different.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to the drawings, the prosthesis P shown in FIG. 1 comprises a glenoidal component 10 which is fixed to the glenoid cavity G by any appropriate means, for example in accordance with the technical teaching of FR-A-2 836 039, and which defines a convex articular surface S₁ substantially in the form of a demi-sphere.

The prosthesis P also comprises a humeral component 20 formed by an anchoring stem 21 and a metaphyseal part 22. The stem 21 is globally rectilinear and adapted to be introduced in the medullary canal M of the humerus H, while the metaphyseal part 22 projects beyond this canal and defines a concave articular surface S₂ in the form of a portion of sphere.

In FIGS. 1, 1A and 2, the glenoid cavity 4 and the component 10 are shown in side view, while the humerus H and component 20 are shown in longitudinal section.

The surfaces S₁ and S₂ are adapted to constitute a sliding articulation and have substantially equal radii.

The external shape of the metaphyseal part 22 is globally cylindrical with circular base and 23 denotes its outer radial surface. Furthermore, 24 denotes its end surface which is globally planar and in which the concave surface S₂ is hollowed. Finally, 25 denotes the outer peripheral edge which connects the surfaces 23 and 24 and which is circular like surface 23.

Central axis X₂₂ of the metaphyseal part 22 is defined by an axis perpendicular to the surface 24 and passing through the imaginary centre of this surface. In practice, axis X₂₂ is an axis of symmetry of the edge 25.

In certain configurations, the surface 24 may be eliminated. In that case, the edge 25 directly joins the surfaces S₂ and 23, and the axis X₂₂ is defined as the axis of symmetry of the edge 25.

The humerus H is assumed to undergo movements of abduction represented by arrow F₁ and movements of adduction represented by arrow F₂ in FIG. 1.

At the end of adduction stroke, those parts of the surface 24 and of the edge 25 most remote from the stem 21 are capable of hitting the pillar of the scapula G₁, i.e. that part of the glenoid cavity G located in the vicinity of the component 10 below the latter when the patient is standing up. In this configuration of interference shown in FIG. 1A, the patient feels discomfort, which is detrimental to the success of the operation.

It will be understood that this configuration of interference is not systematic insofar as the pillar of the scapula G₁ may take different shapes, as shown, in broken lines only, in FIG. 1.

According to the invention, and as is more particularly visible in FIG. 3, a set J of humeral components is provided, in which a plurality of components 20, 20′ and 20″ are prepared with different geometries.

As is visible in FIG. 3, the different components 20, 20′ and 20″ of the set J present globally the same outer shape, their respective stems 21, 21′ and 21″ having substantially the same outer shape, like their metaphyseal parts 22, 22′ and 22″. In particular, the outer radial surfaces 23, 23′ and 23″ of these different metaphyseal parts as well as their edges 25, 25′ and 25″ have substantially the same geometry.

X₂₁ X′₂₁ and X″₂₁ respectively denote the median axes of the anchoring stems 21, 21′ and 21″.

Furthermore, axis X₂ is defined by the axis of symmetry of the surface S₂.

For the component 20, axes X₂ and X₂₂ are merged.

As previously, axis X′₂₂ is defined as the central axis of the metaphyseal part 22′ for the component 20′ and axis X′₂ as the axis of symmetry of the concave surface of articulation S′₂ of the component 20′. Axes X′₂ and X′₂₂ are parallel to each other and offset by a non-zero distance d′. In the same way, axes X″₂₂ and X″₂ are defined as being respectively the central axis of the metaphyseal part 22″ and the axis of symmetry of the surface S″₂, these axes being parallel and offset by a distance d″ greater than distance d′.

α denotes the angle of inclination between the axes X₂₁ and X₂₂, this angle also being the angle of inclination between the axes X₂ and X₂₁ since axes X₂ and X₂₂ are parallel. The angle α′ between axes X′₂₁ and X′₂₂ and the angle α″ between axes X″₂₁ and X″₂₂ have the same value as angle α.

However, such equality of the angles α, α′ and α″ is not obligatory insofar as the axes X₂ and X₂₂, X′₂ and X′₂₂, X″₂ and X″₂₂ are not necessarily parallel.

The different components 20, 20′ and 20″ of the set J are therefore distinguished from one another by the fact that their concave surface of articulation S₂, S′₂, S″₂ is more or less offset with respect to the central axis of their end surface 24, 24′ or 24″. Except for the component 20, the axes X′₂ or equivalent of the concave articular surfaces are closer than the axes X′₂₂ and X″₂₂ to that part of the edge 25 most remote from axis X′₂₁ or equivalent. In other words, the surfaces S′₂ and S″₂ are offset downwardly in FIG. 3 with respect to the median position occupied by the surface S₂ vis-à-vis the surfaces 23 and 24 of the component 20.

The concave surface S″₂ of the component 20″ extends up to the immediate vicinity of the edge 25″ in its part most remote from the stem 21″, this inducing the surface 24″ to be of zero width virtually in this zone. The risks of interferences with the pillar of the scapula G₁ are therefore particularly limited in that case.

In this way, and as shown in FIG. 2, a prosthesis P″ equipped with the component 20″ has less chance of interfering with the pillar G₁ of the scapula, even if the latter has the same geometry as that shown in solid lines in FIG. 1.

When a shoulder prosthesis is installed, the surgeon cuts the bones and pre-positions the glenoidal component or a phantom component. He may then select from the set J the most appropriate humeral component, possibly after testing with phantom components, in order to minimize the risks of interference. In a variant, the surgeon may pre-select the humeral component to be used, during the pre-op check-up.

The invention therefore enables the surgeon, by a reasoned selection of the humeral component 20, 20′, 20″ or equivalent from the set J of components, to adapt the relative position of the glenoidal and humeral components when their respective surfaces of articulation cooperate, while avoiding or limiting to a very considerable degree the interferences between an edge 25 or equivalent of the humeral component and the pillar of the scapula. The invention also makes it possible to “verticalize” the humerus, or render it more vertical, at the end of adduction stroke.

In the set J, the humeral components have substantially the same outer geometry, except for the positioning of their concave articular surface. It is obvious that the different sets J may be provided in different sizes in order to adapt to the morphologies of the patients to be treated, or that a set J of humeral components may incorporate components of different heights. In addition, the number of components of the same set is not limited to three and may take any value greater than two, as a function of the precision desired for the adjustment of the offset d′, d″, etc. . . . .

According to a variant of the invention (not shown), the offset between the axes X₂ and X₂₂ may be even greater than that referenced d″ in FIG. 3, in which case the surface S₂ is intersected by the edge 25. Such a variant makes it possible to offset the surface S₂ downwardly even more, it being understood that the centre of rotation is located on the surface S₂.

As shown in FIG. 4, the milled surface S_(G) of the glenoid cavity is not always parallel to a vertical axis Z-Z′ passing through the centre of the spinal column of the patient in standing position. Now, for a correct cooperation of the surfaces S₁ and S₁, it is preferable if the axis of symmetry X₁-X′₁ of the hemispherical surface S₁ is substantially perpendicular to axis Z-Z′. This is why, in the case of the surface S_(G) being inclined as shown in FIG. 4, a glenoidal component 10, of which the rear face 11 is not perpendicular to axis X₁-X′₁, is used, this making it possible to position the component 10 so that this axis X₁-X′₁ is substantially perpendicular to axis Z-Z′.

The component 10 may be formed by a base 12 and a cap 13, defining the surface S₁ and mounted on the base 12. The rear face 11 of the base 12 is in that case advantageously non-parallel to its front face on which the cap 13 is mounted.

A component 10 as shown in FIG. 4 may advantageously be selected from a set of components presenting variable differences in orientation between their respective rear faces and the axis of the surfaces S₁ that they define.

The invention has been shown with humeral components in one piece. In practice, and according to an aspect of the invention (not shown), the metaphyseal parts of these components are most often equipped with cups made of plastics material defining the surfaces S₂ of these components.

According to a variant of the invention (not shown), the axis of symmetry of the surface S₁ may be offset downwardly when the patient is in standing position, with respect to the axis of symmetry of the base on which the cap defining this surface is mounted.

This may be combined with the non-perpendicularity of the axis X₁-X′₁ and of the rear face of the prosthesis mentioned hereinabove with reference to the form of embodiment of FIG. 4. 

1. Set of humeral components for a total shoulder prosthesis, in which each component is formed by an anchoring stem and a metaphyseal part which defines a concave surface of articulation globally in the form of a portion of sphere, wherein the offset between the axis of symmetry of said surface and the central axis of said metaphyseal part of said components is variable.
 2. The set of components of claim 1, wherein, for each component, said axes are substantially parallel.
 3. The set of components of claim 1, wherein, for at least one of said components, said axis of symmetry is located, with respect to said central axis, opposite a median axis of said stem.
 4. The set of components of claim 3, wherein the surface of articulation of at least one of said components extends up to the immediately vicinity of the edge of said metaphyseal part, opposite that part of said edge located globally in line with said stem.
 5. The set of components of claim 3, wherein the surface of articulation of at least one of said components is intersected by said edge of said metaphyseal part, opposite that part of said edge located globally in line with said stem.
 6. The set of components of claim 1, wherein the different components have substantially the same shape, except for the position of said articular surface in said metaphyseal part.
 7. The set of components of claim 1, wherein the angle of inclination of said axis of symmetry with respect to a median axis of said stem has substantially the same value for all the components.
 8. The set of components of claim 1, wherein for one of said components, said offset is zero, said axes being merged.
 9. Total shoulder prosthesis, wherein it comprises a humeral component selected from the set of components of claim
 1. 10. The prosthesis of claim 9, wherein it further comprises a glenoidal component forming a convex surface of articulation centred on an axis of symmetry which is not perpendicular to a rear face of said component intended to come into abutment against the glenoid cavity.
 11. Method for installing a total shoulder prosthesis comprising steps consisting in: preparing the bones with a view to positioning a glenoidal component and a humeral component; installing on the glenoid cavity a glenoidal component defining a convex articular surface; selecting, from a set of humeral components, a humeral component provided with a concave articular surface adapted to cooperate with a convex articular surface of the glenoidal component, said component substantially not interfering or interfering only little with the pillar of the scapula during a movement of adduction, and installing said humeral component on the humerus. 